The subjects will receive, in random order, either exenatide 10 mg or equivalent volume of saline subcutaneously at 7am on day 2 of the hospitalization (i.e. at -2hr) during the first of the two studies. The pancreatic clamp will begin at 7am (-2hr), immediately following administration of either exenatide or saline and continue throughout the subsequent 12 hours (until 7pm). . During the pancreatic clamp the subjects will receive an iv infusion of glucagon (0.65ng/kg/min), growth hormone (Humatrope, 3.0 ng/kg/min), somatostatin (sandostatin, 25 µg/hr) and insulin (Novolin R, 0.05 mU/kg/min).